1. Field
Some example embodiments relate to an image sensor.
2. Description of the Related Art
An image sensor is a device that includes photoelectric conversion devices and converts light into an electric signal according to the intensity of light received. The image sensor may be used in a digital input device to record non-digitalized images into digital images. The demand for image sensors in digital still and mobile cameras, camera phones, web cameras, and surveillance cameras is increasing with rapidly changing technologies.
The image sensor may include a pixel array including a plurality of pixels arranged in a matrix format, and each pixel includes a light-sensing device and a transmission and signal output device. Although image sensors based on a charge coupled device (CCD) have been a dominant technology, recent advances of image sensors implemented in a complementary metal oxide semiconductor (CMOS) technology have led to their adoption in several high-volume products, such as personal computer cameras, camera phones, and digital cameras, making CMOS image sensors a viable alternative to CCD technology.
Both CCD and CMOS image sensors collect external light through a microlens, and the collected light is transmitted to the light-sensing device such as a photodiode and thus a signal is output. The unique feature of the CMOS image sensor is that each pixel contains transistors to amplify the electrical signal, which provides various advantages such as less noise during signal transition, compact size, faster image processing, lower power consumption, and lower manufacturing cost.
As the demand for higher resolution image sensors increases, pixel size has been reduced to integrate more pixels within the given area. However, as the pixel becomes smaller, the pixels receive a lesser amount of light and the pixel's high aspect ratio allows more crosstalk of the electrical and optical signals, resulting in degraded image quality. Therefore, to keep continuously scaling down the pixels, it is desirable to improve photoelectric conversion efficiency of the pixel and to reduce the crosstalk between pixels in CMOS image sensors.